There's an interesting experiment you can do with 1/2 a grape.
Slice it almost into 2 quarters, leaving a small bit of skin attaching the two quarters, and fold it out. Dry the surfaces. Put it on a plate in the middle of a microwave. Heat for about 10 seconds, until the plasma-ball forms above it as the two halves (and the internal sugars) arc across one another. It pretty much fills the microwave, best when viewed in the dark. Don't know how much this harms the microwave, but I've done it about 20 times in ours. Pretty scary the first time; keep your finger near the "stop" button.